1. Field of the Invention
Apparatuses consistent with the present invention relate to a display panel and a display apparatus, and more particularly, to a display panel and a display apparatus which can obtain excellent visibility by enhancing white balance and out-coupling efficiency with respect to natural light or artificial light from the outside.
2. Description of the Related Art
With the rapid development of communication technologies and display apparatuses, various kinds of portable terminals have been introduced. Examples of portable terminals include personal digital assistants (PDAs), portable multimedia players (PMPs), and digital multimedia broadcasting (DMB) phones. Liquid crystal displays (LCDs) are a type of light-receiving flat panel display (FPD) used in portable terminals. Because LCDs are not self-luminous, they display an image by adjusting the transmittance of light emitted from a light source in each pixel. To this end, backlight units are installed in the rear surface of the LCDs to emit light toward liquid crystal panels.
Backlight units are classified into a direct light type backlight unit and an edge light type backlight unit, based on the arrangement of the light source. The direct light type backlight unit includes a plurality of lamps under the liquid crystal panel, and directly emits light toward the liquid crystal panel. The direct light type backlight unit is suitable for large-sized displays of 30 inches or more, such as LCD televisions (TVs), because the light sources can be freely and efficiently arranged in a wide area without restriction. On the other hand, the edge light type backlight unit is suitable for portable terminals because the light sources are arranged at limited locations, such as the edges of a light guide plate.
Meanwhile, portable terminals may be used in any location because of their portability, and may often be used outdoors in the sunlight. In this case, the visibility of the display may degrade, because the brightness of an LCD screen is relatively dark. Therefore, the advantage of the portable terminals in their ability to be used in any location cannot be sufficiently exploited.
In addition, when the LCD is used for a demonstration display, an outdoor billboard, or in a public place where illumination is present, high utilization of the LCD cannot be obtained if sufficient visibility is not secured.
To solve this problem, a display apparatus operating in both a reflection mode using external light and a transmission mode using a backlight unit has been developed. Such a display apparatus will be referred to as a transflective display apparatus.
FIG. 1 is a cross-sectional view of a related art transflective display apparatus. Referring to FIG. 1, the related art transflective display apparatus includes a light source 10, a light guide plate 15 which guides light emitted from the light source 10, and a liquid crystal layer 47 which adjusts the transmittance of the emitted light. FIG. 2 illustrates one pixel consisting of a blue subpixel B, a green subpixel G, and a red subpixel R. Each of the subpixels has a reflection mode region RM and a transmission mode region TM. The reflection mode region RM is defined by forming a scattering pattern 45 at a portion of the liquid crystal layer 47, and the transmission mode region TM is defined by a portion of the liquid crystal layer 47. A support film 43 is disposed under the scattering pattern 45. A color filter 50 is disposed above the liquid crystal layer 47, and a light hole h is formed in a portion of the color filter 50. The light hole h is formed at a predetermined portion above the scattering pattern 45.
In addition, a first linear polarization film 33, a first quarter wavelength plate 35, a first glass substrate 38, and a thin film transistor (TFT) film 40 are disposed between the light guide plate 15 and the liquid crystal layer 47. A plurality of films 20 are disposed between the light guide plate 15 and the first linear polarization film 33 to enhance light efficiency. The plurality of films 20 may include a diffusion sheet diffusing light, a prism sheet which corrects a light traveling path, and a brightness enhancement film (BEF) which enhances directionality by making the light passing through the prism sheet go directly toward the display panel.
The light Lb illuminated from the light guide plate 15 is incident onto a portion of the liquid crystal layer 47 corresponding to the transmission mode region TM. Then, the light Lb passes through the liquid crystal layer 47, while its transmittance is adjusted based on a voltage of the TFT layer 40. The color filter 50 transmits only a light color within a specific wavelength band. On the other hand, light incident from the light guide plate 15 toward the scattering pattern 45 does not contribute to image formation, because it is reflected. This produces degraded light efficiency; however, the degraded light efficiency is enhanced using external light Ls, so that the LCD can be used in a bright environment. Meanwhile, the external light Ls passes through the color filter 50, and only a light color within a specific wavelength band is transmitted to the scattering pattern 45. The light reflected from the scattering pattern 45 passes through the color filter 50 and is outputted to the outside, thus forming an image. Because the color filter 50 is designed to be optimal for the transmission mode region where a white light emitting diode (LED) is used, color reproduction in the sunlight or external illumination light will be degraded. Furthermore, when the reflection mode is implemented using the external light, the light passes through the color filter 50 two times, resulting in degradation of the light efficiency. To solve this problem, the light hole h is formed in the color filter 50, such that the light is directly incident onto the scattering pattern 45 without passing through the color filter 50. In this way, color reproduction is improved and white balance is adjusted.
FIG. 3A is a graph illustrating color coordinates of light passing through the transmission mode region and light reflected from the reflection mode region. FIG. 3B is a graph illustrating variation of color coordinates for different diameters of the light hole h. It can be seen from FIGS. 3A and 3B that the color coordinate in the reflection mode is similar to the color coordinate in the transmission mode. That is, the color reproduction is enhanced by the light hole.
However, because the scattering pattern 45 scatters and reflects the incident light, the direction of the reflected light is uncontrolled and scattered. Therefore, an amount of light condensed at a user's viewing angle is so small that brightness is low. Although the white balance can be adjusted by varying the size of the light hole h in red, green and blue pixels, increasing the front brightness with high reflection is limited.